In one of the best-known constructions for clamping or tensioning a rubber blanket, the two ends of the blanket are provided with clamping devices which engage in grooves of two tensioning spindles. The blanket is tensioned by turning the spindles via a worm drive by means of a torque spanner. The ends of the blanket are fixed with the clamping devices by the fact that the blanket is screwed between clamping strips. These clamping strips are retained in the tensioning spindle grooves by a positive connection.
When varnishing in a rotary press, it is sometimes necessary to leave some areas of the sheet untouched. For example, on areas of the sheet occupied by adhesive tabs must not be covered by varnish. To accomplish the varnishing in only the desired areas, a varnishing process commonly called selected-area, in-line varnishing is typically employed. For selected-area, in-line varnishing, the offset blanket (required with the direct varnishing method) is usually one in which the top layer of the rubber blanket has been removed at those areas which are not to be varnished. A blanket prepared in this way can also be used for the indirect varnishing method if a plate cylinder is rolled in a dispersion varnish on an aqueous basis over the entire area.
For accurate work, the position of those parts of the varnishing blanket which are not to provide a varnish, (i.e., those parts which are to be cut out) is established by applying to the dry varnish blanket an ink impression of the ink plate thereby providing the guide lines for cutting. To cut out the corresponding area in the blanket is time-consuming and lengthens the downtime. Unclamping the blanket after it has received the ink impression, so that it can be cut out at the same time the ink plates of the in-line press are being made ready is always time-consuming because the blanket has to be reclamped in position.